1. Field of the Invention
This invention relates to batteries, and more particularly to metal air batteries.
2. Description of the Prior Art
Metal-air batteries having an air cathode and a metal or metal alloy anode are increasingly being used for a variety of applications, including the powering of portable electronic equipment such as personal computers.
A major problem with existing metal-air batteries is that the air cathode has a tendency to separate from the electrolyte material over the lifetime of the battery, resulting in the formation of air pockets between the air cathode and the electrolyte. The cause of this separation is as follows. As the metal electrode or anode reacts with the electrolyte during battery operation, a metal oxide or a metal hydroxide is formed. The metal oxide or metal hydroxide has a much larger volume than the metal electrode; the increased volume places pressure on the internal walls of the battery container resulting in an expansion of the container itself. This expansion in turn results in a separation of the air cathode membrane from the electrolyte, and the creation of the air pockets between the air cathode and the electrolyte. The air pockets subtantially interfere with the battery output, and result in premature degradation of the battery.
One attempt to solve the separation problem includes placing a spring at the bottom of the battery container to keep the air cathode membrane and electrolyte layers together. A disadvantage with this approach is that the mechanical spring assembly takes up valuable space within the battery container that would otherwise be used for the active battery materials including the electrolyte and electrodes. The decreased quantities of the active battery materials results in a battery having a lower energy density or smaller output.
Another problem with metal-air batteries is that they require a continuous flow of air across the air cathode membrane for optimal battery operation. The battery's energy output drops dramatically if the flow of air is inhibited or ceases for any reason. It is therefore desirable to provide a metal-air battery whose design enables continuous flow of air across the air cathode membrane.